Today, systems, in which the price indicating items of information are stored in a central system computer, are introduced in greater retail stores, which computer, in turn, provides the cash-point locations with price indicating items of information related to various articles. The cashier normally reads, usually by means of an optical reading device, a unique bar code, the so-called EAN code, which is present on each article. Through this code the cash register thereby obtains the current price information of the article in question from the central system computer.
Further a shelf-edge marking is applied at the location of each article, which marking states the name of the article and normally also a cost-per-unit price, e.g. the price per kilogram. Earlier, each article was usually provided also with a sticker stating the price and possibly a temporary discount price. In order to reduce the cost of such a price marking, effort is made, particularly in larger retail stores, to leave out the individual price marking of each article, in which case the price marking is achieved only by means of shelf-edge marking at the storing place of each type of article.
A further step in cost optimization includes electronic shelf-edge markings, which are controlled from the central system computer, thereby stating the price stored in the central system computer of the article in question. Through this, it will be ensured that the items of information of the price marking will correspond to the price charged to the customer at the cash-point, which obtains the price indicating items of information, just like the shelf-edge marking, from the central system computer. Such systems are hereafter referred to as Electronic Shelf Labelling (ESL) systems and one type of such an system has been disclosed, e.g. in the Swedish patent SE 441 447 granted to S. Olsson and R. Ahlm in 1986.
Common to such systems is that the transmission of information should be achieved via wireless in order to obtain a flexible price-marking system. Such transmission is suitably performed by means of radio or light waves. Preferred radio waves are within the short wave range, mainly due to bandwidth regulations. Preferred light waves are within the range of non-visible light, e.g. IR-light as used in prior art for various remote control devices to control electronic or electrical apparatuses, such as TV-sets etc.
Electronic Shelf Labelling (ESL) systems in retail environments using wireless transmission of data from transmitters to electronic labels (EL) commonly comprise a Base Station (BS) to which a number of transceivers are connected, which BS is capable of issuing messages to be transmitted via said transmitters. The BS is in turn connected to and controlled by a central processing unit, and in special embodiments the BS may even be integrated in the central processing unit. Large systems may further comprise several BS, all connected to the central processing unit. With Transciever (TRX) is meant a combined transmitter and receiver device for electromagnetic radiation (like radio, IR etc) or sound waves or other physical means of distributing signals.
FIG. 1 shows a schematic view of a typical ESL system 10 wherein eight TRX 20 are connected to a BS 30. The TRX 20 is typically connected to the BS 30 by a signal distribution line 40, such as a twisted pair-cable, a coaxial-cable or the like. The coverage area 50 from a single TRX 20 is shown by the solid line, but to obtain maximum coverage, the TRXes are arranged such that constructive interference of signals is used to obtain the required signal-level in the intermediate regions 60 between the coverage areas 50 of two adjacent TRX 20. FIG. 2a shows the principle of constructive interference of signals from two spaced apart TRX 20. The required signal level is shown by L1.
However, as communication frequencies are getting higher, due to a demand for higher transmission capacities and other factors, problems associated with destructive interference or pulse-broadening often arise in the intermediate regions 60. This phenomenon is illustrated in FIG. 2b wherein the part of the resulting pulse that exceeds L1 cannot be detected as a pulse at the receiving end.